1. Field of the Invention
The present invention relates to the demolition of offshore production platforms and more particularly to the removal of the remaining casings, conductors, and piles that may protrude above the sea floor.
2. Description of Prior Art
In the offshore industry, there are many marine structures that support casings and conductors for the production of gas and petroleum. These casings and conductors are tubes of various diameters that extend from deep into the sea floor up to the production deck of the offshore marine structure; they are used as conduits to carry petroleum and gas from a reservoir deep within the earth to a gathering and process location on the offshore marine structure above the sea floor and also above the surface of the sea.
The offshore marine structure is also supported and held in place of the sea floor by round piles. When the offshore marine structure is removed, often the piles are left protruding above the sea floor. To remove the piles, a diver must enter into the pile and cut it below the sea floor. After the pile has been cut below the sea floor, the pile section that protruded above the sea floor and the section that is below the sea floor is removed by a crane located on a surface vessel. This is both expensive and time consuming.
To cut a casing and conductor below the mudline, a cutting tool is placed inside of the casing and conductor and they are cut; care must be taken to keep the casing and conductor in tension at all times to prevent the vertical casing and conductor from collapsing downward onto the cutter blades thereby jamming the blades and further preventing their removal.
When the first inside casing is removed, another cutter with a greater diameter is placed inside of the conductor and it is cut in the same manner as the casing. This procedure is both time consuming and expensive. If there is concrete or grout between the casing and conductor or in the annuals formed by the two tubes, the cutter will not work properly.
If the casing cannot be cut from the inside, it must therefore be cut from the outside and it still must be cut as least fifteen feet (15') below the sea floor. To cut the casing or conductor of pile below the sea floor, a hole must be excavated around the casing and conductor or pile. The excavation must be more that fifteen feet (15') deep to allow a diver to enter into the excavation with sufficient room to cut the casing and conductor of pile. The digging of the excavation is very expensive and time consuming. The cutting of the casing and conductor or pile by a diver from within the excavation is dangerous, time consuming and expensive.
While the diver is cutting the casing and conductor or pile from within the excavation, the casing and conductor or pile could fall over onto the diver. There is also a great danger of the walls of the excavation collapsing on the diver as he cuts the casing, conductor or pile.
There are several other methods of severing and crushing piles, etc. One method is found in a patent issued in the Soviet Union, Patent number PRCS Q42 A6931 E/03 SU-821-653. This is a method of severing concrete piles above a surface such as a sea floor or above the ground on land. This system does not however sever piles below the surface; the piles still remain extending above the surface after they are severed. There is another device that destroys cast iron pipes. This device is shown in U.S. Pat. No. 4,720,211 issued to STREATFIELD et al on Jan. 19, 1988. This method does break up cast iron pipe below the surface of the ground but it does not coil the pipe that is on or above the surface to be buried below the surface of the ground.